Zen freezes when direct descendants of a part element are set to use rtl mode.

[thatcomputerguy0101]

Captchas

• [X] I have read the instructions.
• [X] I have searched existing issues and avoided creating duplicates.
• [X] I am not filing an enhancement request.

What happened?

The browser freezes whenever the following styles are applied through a Zen Mod chrome.css, but not when they are applied through userChrome.css. This is relying on a beneficial bug with user agent stylesheets where descendant selectors relative to the part selector work whenever structured as nested blocks. Normally, using descendant selectors relative to a part selector is disallowed. Ideally, only the freeze is fixed, and the ability to use descendant selectors in this format is left alone.

#tabbrowser-arrowscrollbox::part(scrollbox) {
  & > * {
    direction: rtl;
  }
}

Reproducible?

• [ ] I have checked that this issue cannot be reproduced on Mozilla Firefox.

Version

1.0.1-a.17

What platform are you seeing the problem on?

macOS - aarch64

Relevant log output

No response

[dosubot[bot]]

The issue you're experiencing with Zen Mod freezing when applying direction: rtl; to direct descendants of a ::part() element seems to be related to how Zen Mod handles CSS differently compared to userChrome.css. Zen Mod dynamically manages themes and integrates with user preferences, which might be causing the freeze when using certain CSS structures that are not typically allowed, like descendant selectors relative to a ::part() selector ^[1].

Since this issue does not occur with userChrome.css, it suggests that the dynamic nature of Zen Mod's CSS handling might be conflicting with the specific CSS rules you're applying. Unfortunately, there isn't specific information available about handling direction: rtl; or ::part() in the Zen Mod codebase, so a workaround might involve restructuring your CSS to avoid using descendant selectors in this context or testing on different platforms to see if the issue persists.

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